FIGS. 1, 2, 2A, 3 and 4 of this specification represent prior art which is described herein to convey the distinction between prior art seals and the present invention.
Referring now to the prior art of FIG. 1 there is shown a cross-sectional view of a hydrodynamically lubricated interference type rotary shaft sealing assembly generally at 1 including a housing 2 from which extends a rotary shaft 3. The housing defines an internal seal installation groove or gland 4 within which is located a ring shaped hydrodynamic rotary shaft seal 5 which is constructed in accordance with the principles of U.S. Pat. Nos. 4,610,319 and 5,230,520, and which is shown in greater detail in FIGS. 2, 2A and 3. The hydrodynamic seal separates the lubricant 6 from the environment 7, and prevents intermixing of the lubricant and the contaminant matter present in the environment.
FIG. 2 represents the radially uncompressed cross-sectional shape of the prior art seal 5, FIG. 2A represents the cross-sectional configuration of the prior art seal 5 when located within its seal groove and radially compressed between the outer diameter 14 of the rotary shaft 3 and the radially outer wall 11 of the seal groove, and FIG. 3 shows the footprint made by the dynamic sealing lip 12 against the shaft. The environment usually contains highly abrasive particulate matter in a fluid; an example of such an environment would be oil field drilling fluid. From an overall orientation standpoint, the end of the seal which is oriented toward the lubricant is surface 8 and the end of the seal which is oriented toward the environment 7 is surface 9. When the seal 5 is installed in the circular seal groove or gland 4, a circular radially protruding static sealing lip 10 is compressed against a counter-surface 11 of the groove per the teachings of U.S. Pat. No. 5,230,520. At the inner periphery of the circular sealing element 5 there is provided an inner circumferential sealing lip 12 that defines a dynamic sealing surface 13 that is compressed against a cylindrical sealing surface 14 of the rotatable shaft 3. The circular seal groove or gland 4 is sized to hold the resilient circular sealing element 5 in radial compression against the cylindrical sealing surface 14 of the shaft 3, thereby initiating a static seal with the housing and shaft in the same manner as any conventional interference type seal, such as an O-Ring. When shaft rotation is not present, a liquid tight seal is maintained at the static sealing interface between the static sealing lip 10 and the mating counter-surface 11 of the seal groove, and between the dynamic sealing lip 12 and the cylindrical sealing surface 14 of the shaft.
When shaft rotation takes place, the hydrodynamic seal remains stationary with respect to the housing, and maintains a static sealing interface with said housing, while the seal-to-shaft interface becomes a dynamic sealing interface. The inner peripheral surface of the seal inner lip 12 incorporates a geometry that promotes long seal life by hydrodynamically lubricating the dynamic seal-to-shaft interfacial zone, and by excluding environmental contaminates from the seal to shaft interface. Seal lip 12 incorporates a wavy edge 15 on its lubricant side, and an abrupt circular edge 16 on its environmental side per the teachings of U.S. Pat. No. 4,610,319. For the purpose of orienting the reader, the radial cross-section of all seal cross-sectional figures herein is taken at a circumferential location which represents the average width of the wavy dynamic sealing lip contact shown in FIG. 3. As relative rotation of the shaft takes place, the wavy edge 15 on the lubricant side of the dynamic sealing lip, which has a gradually converging relationship with the shaft, generates a hydrodynamic wedging action that introduces a lubricant film between the seal inner surface 13 and the cylindrical sealing surface 14 of the shaft per the teachings of U.S. Pat. No. 4,610,319. This lubricant film physically separates the seal and the shaft, and thereby prevents the typical dry rubbing type frictional wear and heat damage associated with conventional non-hydrodynamic interference type seals, and thereby prolongs seal life and mating shaft surface life and makes higher service pressures practical. This hydrodynamic action, which is described in detail in U.S. Pat. No. 4,610,319, can more easily be understood by referring to FIG. 3, which shows a flat development of the cylindrical sealing surface 14 of the shaft, and which depicts the footprint of the dynamic inner lip 12 of the seal against the cylindrical sealing surface 14 of the shaft. From an orientation standpoint, the lubricant is shown at 6, the seal footprint is shown at 17, and the environment is shown at 7. The lubricant side of the footprint has a wavy edge 18 created by the wavy edge 15 of the seal, and the mud side of the footprint has a straight edge 19 created by the abrupt circular corner 16 of the seal. The lubricant is pumped into the dynamic sealing interface by the normal component VN of the rotational velocity V.
Referring again to FIG. 2 and FIG. 2A, the abrupt circular corner 16 of the environmental side of the hydrodynamic is not axially varying, and does not generate a hydrodynamic wedging action with the environment in response to relative rotary motion, and thereby functions to exclude particulate contaminants from the seal-to-shaft interface per the teachings of U.S. Pat. No. 4,610,319.
The illustration of FIGS. 2 and 2A illustrates the customary type of general purpose hydrodynamic rotary shaft seal that positions and configures the exclusionary edge 16 and the environmental end 9 of the seal 5 in such a manner that lip 12 is largely supported by the environment-side gland wall 20 in a manner that resists distortion and extrusion of seal material when the seal is subjected to the hydrostatic force resulting from the lubricant pressure acting over the annular area between the static sealing interface and the dynamic sealing interface. Such force occurs when the lubricant pressure is higher than the environment pressure. FIGS. 1 and 2A illustrate the seal being forced against the environment-side gland wall 20 by hydrostatic force resulting from the lubricant pressure acting over the area between the static sealing interface and the dynamic sealing interface.
The static sealing lip 10 has generally the same cross-sectional geometry as the average cross-sectional configuration of the dynamic sealing lip 12 except that it is shorter. Because both lips have the same general shape and axial location, when the seal is compressed, the interfacial contact force profiles and deformation of the two lips are very similar in both their magnitude and axial location per the teachings of U.S. Pat. No. 5,230,520, and as a result, there is no gross tendency for the seal to twist counter-clockwise within the gland in the absence of lubricant pressure. The magnitude of projection 21 is designed so that lip 10 is flattened out against mating counter-surface 11 of the gland upon installation so that contact between the outer periphery of the seal and the gland surface provides mechanical stability against seal twisting in unpressurized applications. The magnitude of projection 12 is designed to be larger than projection 21 so that dynamic lip 22 is not overly flattened and deformed against the shaft upon installation so as to preserve the form and function of the hydrodynamic inlet geometry 15.